Investments Accounted for by the Equity Method and Variable Interest Entities - Equity Method Investments (Details) - USD ($) $ in Millions	3 Months Ended									12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017		Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Total operating revenue	$ 229	$ 292	$ 307	$ 225	$ 231		$ 269	$ 288	$ 221	$ 1,053	$ 1,009	[1]	$ 1,035
Operating income	54	100	144	49	20		84	125	54	347	283	[1]	222	[1]
Net loss	(91)	$ 49	$ 96	$ 0	(97)		$ 31	$ 44	$ (2)	54	(24)	[1],[2],[3]	2	[1],[2],[3]
Current assets	756				482	[4]				756	482	[4]
Current liabilities	704				540	[4]				704	540	[4]
Non-current liabilities	5,572				5,790	[4]				5,572	5,790	[4]
GCE Holding LLC
Schedule of Equity Method Investments [Line Items]
Total operating revenue										65	71		72
Operating income										32	36		38
Net loss										22	26		26
Current assets	43				38					43	38
Non-current assets	358				374					358	374
Current liabilities	22				18					22	18
Non-current liabilities	182				189					182	189
Desert Sunlight
Schedule of Equity Method Investments [Line Items]
Total operating revenue										208	207		211
Operating income										129	127		129
Net loss										84	80		80
Current assets	133				133					133	133
Non-current assets	1,298				1,350					1,298	1,350
Current liabilities	58				64					58	64
Non-current liabilities	962				1,003					962	1,003
NRG DGPV Holdco
Schedule of Equity Method Investments [Line Items]
Total operating revenue										69	37		14
Operating income										23	7		2
Net loss										11	(3)		0
Current assets	79				74					79	74
Non-current assets	784				671					784	671
Current liabilities	84				83					84	83
Non-current liabilities	314				216					314	216
Redeemable Noncontrolling Interest	0				44					0	44
RPV Holdco
Schedule of Equity Method Investments [Line Items]
Total operating revenue										14	16		13
Operating income										0	3		2
Net loss										0	3		2
Current assets	2				3					2	3
Non-current assets	173				183					173	183
Current liabilities	1				0					1	0
Non-current liabilities	8				7					8	7
Redeemable Noncontrolling Interest	26				16					26	16
Investments, Other
Schedule of Equity Method Investments [Line Items]
Total operating revenue										249	247		193
Operating income										103	89		71
Net loss										75	56		$ 38
Current assets	148				139					148	139
Non-current assets	2,511				2,621					2,511	2,621
Current liabilities	58				60					58	60
Non-current liabilities	$ 889				$ 932					$ 889	$ 932

[1] Retrospectively adjusted as discussed in Note 1, Nature of Business.

[2] Retrospectively adjusted as discussed in Note 1, Nature of Business.

[3] Retrospectively adjusted as discussed in Note 1, Nature of Business.

[4] Retrospectively adjusted as discussed in Note 1, Nature of Business.